I dont think they are as quick to build up either as some of the other breeds.
The thing with russians is they wont build number up very fast on syrup. The need natural nectar. When there is a stong flow, russians will build up very fast. Much faster than other breeds. In a strong flow I have run three deeps with supers to accomodate. Russian can swarm more than one a year and even a 1st year package can swarm.
The queen shuts down laying much sooner in the fall that other breeds. This could also be a added benefit the varroa battle. That also leads to the small winter cluster. They dont need to be as heavy int he winter. I have seen russians survive a mild new england winter on 20lbs of honey and 30lbs in a normal winter.